Field of the Invention
The present invention relates to the control of signals in an envelope tracking amplification stage.
Description of the Related Art
Envelope tracking amplification stages are well-known in the art, in which a power supply to a power amplifier is controlled to be based upon the envelope of an input signal to be amplified. The power amplifier receives the input signal to be amplified, and in addition receives a power supply which is modulated in dependence upon the envelope of the input signal to be amplified. An amplified output signal is thus generated in an efficient way.
It is known in the art to provide processing in the envelope path in order to shape the envelope signal which controls a modulator for generating a power supply for the power amplifier.
It is also known in the prior art to provide delays in either the input path to the power amplifier or the envelope path for the supply to the power amplifier, in order to ensure that the instantaneous power supply delivered to the power amplifier corresponds to the instantaneous level of the input signal.
For the purposes of discussion it is assumed that there is no inherent delay difference between the envelope and (RF) input paths.
When an RF envelope has a positive slope, a delay in the supply voltage means that the supply voltage is a little below the desired target level, therefore preventing the RF output envelope from reaching its target as the output is similarly a little low. On the same basis, when the RF envelope has a negative slope, a delay in the supply voltage means that the RF output envelope is slightly too high.
If a delay is applied to the RF envelope signal, then when the RF envelope has a positive slope, the delay in the supply voltage means that it is a little above target, therefore forcing the RF output envelope to be above its target. On the same basis, when the RF envelope has a negative slope, the delay in the supply voltage means that the RF output envelope is slightly too low.
It is an aim of the present invention to provide a basis for controlling a delay applied in an envelope tracking amplification stage to improve efficiency.